Exhaust modulator

ABSTRACT

An exhaust modulator in or to be fitted in the exhaust system of an engine, having a body defining a flowpath therethrough for engine exhaust gases, a gate in the exhaust flowpath movable between an open and a closed position, one or more bleed flowpaths communicating between opposite sides of the gate, and a flow control mechanism. The mechanism is responsive to one or more operating parameters to control the flow of exhaust gases along the one or more bleed flowpaths so as to limit the back pressure applied to the engine to different predetermined levels as required for operation of the modulator in selected modes.

This invention relates to an exhaust modulator, in particular for use inthe exhaust system of a commercial diesel engine vehicle.

Devices known as `exhaust modulator valves` can be fitted into thevehicle exhaust system, which by generating a back pressure can assistthe vehicle in braking, assist in cab heating by giving a faster enginewarm up, or assist in exhaust emission control.

In general, the greater the back pressure generated the more effectivethe braking effect becomes. But the maximum level of back pressuregenerated must be held at a level conducive to the engine, dependingupon the loads generated by the valve springs for example.

To limit the back pressure, the exhaust brake gate, normally a butterflyvalve or a sliding gate must either be locked into a position which isalmost closed, allowing some exhaust gas to escape or have one or morebleed holes formed in the butterfly or sliding gate. It is usual inpractice to drill a hole or holes, (the latter method), and allow thebutterfly or gate to sit in a fully closed position.

The leakage rate is fixed by the size and number of holes in thebutterfly and is dictated by the maximum allowable back pressure whenthe engine is running at the higher speeds and the flow of exhaust gasthrough the exhaust brake is at its maximum.

It follows that at lower engine speeds, especially in the normal drivingrange the `bleed holes` in the butterfly or gate are larger than isnecessary to reach the maximum back pressure at these lower speeds.

U.S. Pat. No. 4,682,674 discloses an exhaust modulator or exhaust-typeengine suppressor in which the maximum back pressure imposed thereby islimited by means of a pressure-relief valve operable to admit flow ofexhaust gases along a bleed flowpath only when a prescribed backpressure is reached. The valve is spring loaded so as to open by anamount which varies depending upon the amount by which the prevailingback pressure exceeds the prescribed limit.

An exhaust modulator for use in cab-heating or emission control isrequired to operate at low engine speeds and hence low exhaust gasflows, whereas for exhaust braking the engine is normally operating ahigh speed and exhaust gas flow rates, the maximum permissible backpressure being relatively high in the latter case.

One object of the present invention is to provide an exhaust modulatorsuitable for use in various modes, more particularly in a cab-heatingand/or emission control mode as well as in an exhaust braking mode.

In accordance with the present invention, we propose an exhaustmodulator having means for controlling the flow of exhaust gases alongone or more bleed flowpaths to achieve different predetermined levels ofback pressure imposed upon the engine, as required to operate inselected modes, said flow control means being operable in response toone or more sensed engine operating parameters.

In accordance with a preferred embodiment of the invention an exhaustmodulator in, or to be fitted in, the exhaust system of an engine,particularly a diesel engine in a commercial vehicle comprises a bodydefining therethrough a flowpath for engine exhaust gases, a gate in theexhaust flowpath, one or more bleed flowpaths communicating betweenopposite sides of the gate and flow control means operable in use, inresponse to one or more sensed engine operating parameters, to controlthe flow of exhaust gases along the said one or more bleed flowpaths soas to limit the back pressure applied to the engine to differentpredetermined levels as required for operation of the modulator inselected modes.

Thus, the flow of exhaust gas along the bleed flowpath is variable inaccordance with the operating conditions pertaining, to achieve anydesired back pressure/exhaust gas flow characteristic or profile. Thecharacteristic or profile may be varying but in the preferred embodimentis stepped between the said first and second predetermined levels, inaccordance with predetermined control data or settings appropriate to orrepresentative of the conditions prevailing or to be achieved, the typeand level of sophistication of the control means being selectedaccordingly. For example, the control means may be directly responsiveto one or more of the said operating parameters. Alternatively, anexternal control system responsive to sensing means and optionallyprogrammed or programmable to vary the flow in accordance with storeddata representative of a desired operating characteristic or profile maybe used.

In one embodiment in which flow along the bleed flowpath or flowpathsmay be regulated directly, the flow control means automatically sensesthe level of back pressure prevailing upstream of the gate and adjuststhe effective flow area of the bleed flowpath to a point at which adesirable back pressure is reached appropriate to any engine speedand/or exhaust gas through flow.

The flow control means may comprise a valve biased toward a closedposition, that is a position wherein communication via the bleedflowpath is cut off, and, further, may incorporate stop means limitingthe effective flow area to a predetermined maximum value. The valve maycomprise a disc biased toward and cooperating with a valve seat to shutoff the bleed flow but is preferably a simple reed or flap valvecovering a bleed hole and biased by virtue of its inherent resiliencetoward the closed position. Multiple valves arranged in parallel andhaving different bias stiffnesses or one valve having a stepped varyingstiffness, or both in combination may be used to achieve the desiredstepped characteristic or profile. The latter arrangement may beachieved using compound springs.

Another embodiment in which `external` control is used comprises a gatein the exhaust flowpath, a bleed flowpath communicating between oppositesides of the gate, sensing means for producing signals representative ofone or more operating parameters, the flow control means beingresponsive to said signals and operable, in use, to control flow alongthe bleed flowpath.

The sensing means may sense exhaust gas back pressure .and in additionor alternatively one or more other parameters, for example temperature,speed, exhaust emissions and oil pressure. For example, in the cabheating mode the exhaust modulator serves to impose a back pressure onthe engine to achieve faster engine warm up. By virtue of an embodimentof the invention, control of this procedure is possible by varying flowalong the bleed flowpath in response to the sensed cab temperature.

Also, as the exhaust gas flow rate tends to increase with engine speed,the exhaust gas bleed flow (and hence applied back pressure) mayadvantageously be varied in response to an engine speed sensor.

It will be understood that external control is possible by usingmechanical, pneumatic, hydraulic electric or electronic control means orany combination thereof. Clearly, the choice of systems or componentsthereof will depend upon the facilities and, power sources available onthe vehicle and the parameters to be sensed.

As in conventional exhaust brakes, the gate is preferably a butterflyvalve and may have one or more bleed holes therein to provide the bleedflowpath. Alternatively, the or each bleed flowpath may be a by-passchannel leading from one side of the gate to the other and may be formedin the exhaust brake body or fitted externally thereof or indeed, may beprovided in any convenient manner. External fitting is particularlyappropriate in the case of the `external` control embodiment.

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 shows schematically a conventional engine exhaust system;

FIG. 2 shows to an enlarged scale, and in cross-section, an exhaustbrake body forming part of the system of FIG. 1;

FIGS. 3A and 3B are cross-sectional views of a bleed flow control valveaccording to the present invention, respectively under low and mediumback pressure conditions;

FIG. 3C is a view on arrow A in FIG. 3A;

FIG. 4 is a view similar to FIG. 3A, of an exhaust modulator includingvariable orifice limit stops;

FIGS. 5A to 5C are views similar to FIGS. 3A to 3C but of a modifiedexhaust modulator incorporating reed straps;

FIGS. 6A to 6C are views similar to FIGS. 3A to 3C of another embodimentof exhaust modulator; and

FIGS. 7A and 7B are cross-sectional views of another embodiment ofexhaust modulator respectively under low and high back pressureconditions.

FIGS. 8A to 8C illustrate different operating states of an exhaustmodulator having a double reed valve adapted to provide stepped control;

FIG. 8D and 8E illustrate a single reed valve embodiment,: FIG. 9 is ablock diagram of an exhaust modulator control system;

FIG. 10 is a cross-section showing the actuator of the exhaust modulatorin the system of FIG. 9;

FIG. 11 shows the bleed flowpath in the exhaust modulator of FIG. 10, toan enlarged scale; and

FIGS. 12A to 12C show an actuator similar to that of FIG. 10 but adaptedto adjust the flow along the bleed flowpaths by varying the effectiveflow area thereof.

The conventional system shown in FIGS. 1 and 2 incorporates abutterfly-type modulator gate 24 mounted within a modulator housing 10defining an internal flowpath and connected in the exhaust line betweenthe engine 12 and silencer 14. A shaft 23 is rotatably mounted in thehousing 10 and connected to an actuator (not shown) whereby thebutterfly gate 24 is pivotally displaceable between an open position(not shown) and a closed position (see FIG. 2). A bleed hole 26 isprovided in the gate 24 to limit the back pressure imposed upon theengine.

In the following, various forms of the exhaust modulator according tothis invention are described. All of the embodiments illustratedincorporate an exhaust modulator gate of the butterfly type but wouldequally apply to a sliding exhaust modulator gate.

The exhaust modulator of FIGS. 3A to 3C comprises a butterfly-type gate44 mounted in an exhaust gas flow path through the exhaust modulatorhousing 10, on a rotatable shaft 43 driven by an actuator (not shown)whereby the gate 44 can be opened or closed, to impose back pressureupon the engine when required for purposes of cab-heating or emissioncontrol or for exhaust braking. To limit the imposed back pressure twobleed-holes 46 are formed in the butterfly gate 44, these being coveredby strip-like reeds 41 and 41" attached to the shaft 43 by fixing screwsor rivets 45, to prevent the flow of exhaust gas through the bleed holes46 and thus causing back pressure to increase on the upstream side ofthe gate 44.

The reeds 41 and 41' have different stiffnesses selected such that, thereed valve 41 opens to permit exhaust gas to flow downstream through thebleed hole 46 when the maximum desirable pressure level appropriate tothe cab-heating or emission control operating mode (i.e. low enginespeed/low exhaust gas flows) is reached. Reed 41', however, remainsclosed.

After use for this purpose, it is usual to operate the actuator (notshown) to open the gate, so that the engine continues to run in theusual manner.

When exhaust braking is required, this normally occurring at high enginespeeds and high exhaust gas flows, the actuator (not shown) is operatedto close the gate and, as in the cab-heating mode, back pressure buildsup but more rapidly. The reed 41 will open almost as soon as the valveis closed, permitting limited leakage through the bleed hole 46insufficient to prevent an increase in back pressure which furtherincreases up to the desired maximum determined by the stiffness of thesecond reed 41' which then opens providing an increased effective bleedflow path area; the total of the cross-sectional areas of the two holes46.

The exhaust modulator of FIGS. 3A to 3C provides a stepped backpressure/engine exhaust gas flow profile enabling effective andefficient operation of the modulator, either in a cab-heating oremission control mode or in an exhaust brake mode as required.

FIG. 4 shows a similar modulator having two reeds 61 and 61' ofdifferent stiffness but fitted with reed stops 67 and 67' respectivelywhich can be set or adjusted as required to limit opening of the reedmore than is desirable should the unit be fitted to an engine with anexhaust gas flow greater than the reed's design specification, or moreimportantly to limit the effective flow area of each bleed flowpath,enabling fine adjustment of the stepped characteristic or profile tosuit a particular installation.

A sliding reed arrangement is used in the exhaust brake illustrated inFIGS. 5A to 5C. It has two reeds 71 one of which is significantlystiffer than the other. Each reed 71 and a strap 78 overlying the reed71 are clamped at one end but the reed is allowed to slide relative tothe strap 78 by means of an open-ended slot in the reed at the other.Each reed 71 covers two bleed holes 76 drilled in the butterfly 74, andas the back pressure increases the reed 71 lifts towards the concaveunderside of the strap 78 allowing exhaust gas to escape as illustratedin FIG. 5B.

An alternative exhaust modulator valve arrangement shown in FIGS. 6A to6C incorporates two discs 81 each covering a single bleed hole 86 andloaded by a coil spring 88 disposed within a housing attached to thebutterfly 84 for displacement therewith. The disc 81 seals against theseat 89 formed in the butterfly valve 84. As the back pressureincreases, the disc 81 moves away from the butterfly 84, allowingexhaust gas to escape downstream of the engine through passage 90. Withincreasing through flow of exhaust gas, the spring 88 becomes furthercompressed and the orifice area increases as shown in FIG. 6B.

Operation of the embodiments of FIGS. 5A to 5C and FIGS. 6A to 6C, is,in principle, the same as for the embodiments of FIGS. 3A to 3C. Bothprovide a stepped back pressure characteristic or profile enabling useof the modulator in different operating modes without loss ofefficiency.

As stated above, the bleed flowpath or flowpaths may be formed in thebody of the exhaust modulator and one example of such a construction isillustrated in FIGS. 7A and 7B. A boss 98 on the side of the exhaustmodulator body is capped by a sealing bolt 99 to define a cavity 100communicating between a drilling 96 on the up-stream side of thebutterfly 94 and a drilling 97 on the down-stream side of the butterfly.The former drilling 96 is covered by a reed valve 91. When the volume ofexhaust gas increases and back pressure increases the reed valve 91opens as shown in FIG. 7B. The amount of reed valve 91 deflectiondetermines the effective flow area of the bleed flowpath. Exhaust gaspassing through the variable orifice moves into the area downstream ofthe butterfly 94 via the cavity 100 and the drilling 97.

It will be understood that as with the embodiments of FIGS. 5A to 5C andFIGS. 6A to 6B, the use of multiple flowpaths fitted with reeds ofdifferent stiffness a stepped response can be achieved.

The exhaust brake of FIGS. 8A to 8C has two reeds 101, and 101', whichmay be identical, separated by a spacer, the three parts fitting into aslot 102 in the shaft 103, and are secured by fixing screws or rivets105. The thickness, stiffness and other characteristics of the reeds andspacer can be varied as appropriate for a particular application. Reed101 lies flat against the butterfly valve plate 104 covering hole 106 asshown in FIG. 8A preventing the escape of gas. As back pressurebuilds-up reed 101 deflects to open a bleed orifice which grows largeras the pressure increases to increase the exhaust gas through-flow,until reed 101 comes into abutment with reed 101' so that the compoundstiffness is then effective. It will be evident that this arrangementproduces a change in the gradient of the back pressure/exhaust gas flowcharacteristic, at the point of abutment of the two reeds, so thatfurther increases in back pressure give rise to slower increase in thesize of the bleed orifice, producing a stepped or quasi-stepped responsecharacteristic. If the reed 101' is significantly stiffer than reed 101,the response will be substantially flat until the maximum back pressurein exhaust braking mode is reached.

In the single reed arrangement of FIGS. 8D and 8E, the reed 111 is setcentrally (of the cross-section) in the hole 116 in the butterfly valveplate 114. On its downstream side the periphery of the hole 116 ispartially countersunk as illustrated such that as the back pressureincreases (FIG. 8E) the size of the bleed orifice is increasedcontinuously and more rapidly than the single reed arrangement shown inFIGS. 3A to 3C producing a less steeply curved back-pressure/exhaust gasflow characteristic.

One example of an `external` control system for control of an exhaustmodulator is shown in FIG. 9. Detectors or sensors 121 for sensingvarious (in this case engine) operating parameters are connected tosupply signals to a central control unit which may be a computer 122which in turn generates a control output signal to drive an actuator 124for the exhaust brake via a control valve 125. The type of sensors 121used will naturally depend upon the parameters to be monitored and theactuator may be of any conventional kind depending upon whether abutterfly or sliding exhaust brake gate is used. Mechanical, hydraulic,pneumatically, vacuum or solenoid operated, or indeed any suitableactuator may be used. It may be effective to control exhaust gas flowalong the bleed flowpath(s) by adjustment of the effective flow areathereof in a manner analogous to the embodiments described above or mayoperate in response to a pulsed signal to relieve back pressuredirectly; effectively operating as a closed loop control system when(one of) the sensed parameter(s) is the back pressure applied to theengine.

FIGS. 10 and 11 show a typical actuator serving merely to open or closethe bleed flow path as necessary in accordance with a predeterminedprogram stored in the central (computer) control unit and in response tosensed operating parameters. The actuator is built into the exhaustmodulator housing and may be operable, for example, by air or hydrauliccontrol signals to control the pressure applied to control signal port130 to act upon a biased piston or plunger 132, causing the plunger torise against the action of the spring 134 thus opening the bleedflowpath 136 (see FIG. 11) communicating between opposite sides of thebutterfly valve plate 138 shown in the closed position. An adjustingscrew 140 permits the force applied by the spring 134 to be varied.

The use of the multiple bleed flowpaths each fitted with an actuatorsuch as described with reference to FIGS. 10 and 11 but operable underdifferent conditions, will produce a stepped back pressurecharacteristic or profile.

Alternatively, a stepped response can be achieved by means of an exhaustmodulator having a single actuator 121 such as shown in FIGS. 12A to 12Cwhich is built into the exhaust modulator housing and operable by afluid control signal applied to a control signal port 150 communicatingwith a cylinder 152 to act upon a piston 154 biased by a spring 156. Twosets of bleed flowpaths 158 and 160 connect the cylinder 152 to oppositesides of the butterfly valve plate 162 shown in the closed position. Theflowpaths 158 as illustrated have a greater effective flow area than thebleed flowpaths 160.

At low pressure, a signal from the control valve 125 (FIG. 9) lifts thepiston 154 against the spring 156 to uncover and interconnect theflowpaths 160 allowing a limited bleed flow from one side of thebutterfly valve to the other as shown in FIG. 12B. Under differentconditions, say at higher pressure, the signal pressure is increased tothe point at which the piston 154 lifts to the position shown in FIG.12C, sufficiently to uncover and interconnect the flowpaths 158. Theexhaust modulator is thus operable to achieve a stepped back pressurecharacteristic.

We claim:
 1. An exhaust modulator for an exhaust system of an internalcombustion engine, comprising a flow control means operable to controlthe flow of exhaust gases along at least one bleed flowpath so as toachieve different predetermined rates of increase of back pressure withincreasing engine r.p.m., said flow control means being operable inresponse to at least one operating parameter.
 2. An exhaust modulatoraccording to claim 1 wherein the flow control means are operable inresponse to engine operating parameters.
 3. An exhaust modulatoraccording to claim 1 wherein the rate of flow of exhaust gas throughsaid at least one bleed flowpath is varied to produce a relatively lowback pressure to assist in engine warm up and a relatively high backpressure to facilitate engine braking.
 4. An exhaust modulator accordingto claim 1 wherein operation of the flow control means is governed bythe rate of flow of exhaust gas.
 5. An exhaust modulator according toclaim 1 wherein the flow control means further comprises at least onereed valve.
 6. An exhaust modulator according to claim 5 furthercomprising a first reed valve having a certain stiffness and a secondreed valve having a higher stiffness than the first reed valve.
 7. Anexhaust modulator according to claim 6 wherein the second reed valve isarranged to control movement of the first reed valve.
 8. An exhaustmodulator according to claim 6 wherein a stop is provided to limitmovement of at least one of said reed valves.
 9. An exhaust modulatoraccording to claim 8 wherein the stop is in the form of a strapoverlaying at least one of said reed valves.
 10. An exhaust modulatoraccording to claim 1 wherein the flow control means comprises an orificedefining a bleed flowpath and a disc biased toward said orifice to closethe bleed flowpath.
 11. An exhaust modulator according to claim 10wherein more than one orifice and biased disc is provided, each discbeing biased by resilient means of different stiffness.
 12. An exhaustmodulator according to claim 10 wherein each disc is biased by resilientmeans having a different preload.
 13. An exhaust modulator for anexhaust system of an internal combustion engine, comprising a bodydefining a flowpath therethrough for engine exhaust gases, a gate in theexhaust flowpath movable between an open and a closed position and atleast one bleed flowpath communicating between opposite sides of thegate, and a flow control means operable to control the flow of exhaustgases along said at least one bleed flowpath so as to limit the increaseof back pressure applied to the engine to different predeterminedincreasing rates as engine r.p.m. increases, as required for operationof the modulator in selected modes, said flow control means beingoperable in response to at least one operating parameter.
 14. An exhaustmodulator according to claim 13 wherein said at least one bleed flowpathextends as a by-pass channel (96, 100, 97) through the body.
 15. Anexhaust modulator according to claim 14 wherein said at least one bleedflowpath is adapted to be closed by a valve including at least one flowport and piston movable to close the port.
 16. An exhaust modulatoraccording to claim 15 wherein bleed flowpaths having differentcross-sectional areas are provided.
 17. An exhaust modulator accordingto claim 13 including sensing means for producing signals representativeof said at least one operating parameter, the flow control means beingresponsive to the signals to control the flow along said at least onebleed flowpath.
 18. An exhaust modulator according to claim 17 whereinthe sensed operating parameter is one of exhaust gas back pressure,engine temperature, vehicle cab temperature, engine speed, vehiclespeed, exhaust emissions and engine oil pressure.
 19. A method ofoperating an exhaust modulator comprising a body defining a flowpaththerethrough for engine exhaust gases, a gate in the exhaust flowpathwhich is movable between an open and a closed position; at least onebleed flowpath communicating between opposite sides of the gate, andflow control means operable to control the flow of exhaust gases alongsaid at least one bleed flowpath the method comprising sensing at leastone operating parameter and operating the flow control means in responseto said at least one operating parameter to change the rate of increaseof back pressure imposed on the engine with increasing engine r.p.m.